InetAddress.get*() vs RFC 6724

[Alan Bateman]

On 06/02/2026 10:08, Robert Stupp wrote:
> Hi all,
>
> I wanted to test for the appetite to change the current default 
> behavior of the IP address lookup policy on dual-stack (IPv4+IPv6) 
> systems.
>
> The default evaluated in InetAddress.initializePlatformLookupPolicy() 
> yields 'IPV4_FIRST' to return IPv4 addresses before IPv6 addresses 
> unless 'java.net.preferIPv6Addresses' is set to 'true'. I wonder 
> whether this could be changed to the system default, relying on what 
> 'getaddrinfo' returns?
>
> This would make Java compliant with RFC 6724, which (strongly) 
> recommends to yield IPv6 addresses first.
>
> Naively speaking, it can be confusing if something like 'curl' or 
> 'wget' connect via IPv6, but any Java application connects via IPv4.
>
> Although it's a tiny code change, it would be a "big" or "surprising" 
> behavior change. Therefore I think, if there's appetite for such a 
> change, it would need to go into one of the next major releases.
>
> WDYT?
>

Moving to net-dev as that is where the networking APIs are maintained.

As an initial comment, changing the JDK to prefer IPv6 addresses by 
default would be a significant and observable change. TBH, I don't see 
this being changed without a wide survey of configurations and a JEP 
that lays out the case and implications of the change.

Is your motive for asking solely because curl/wget tools prefer IPv6? 
I'm wondering if there is more to the question, maybe HTTP protocol 
handler or client only using the first address?

-Alan